1. PROJECT SUMMARY The regeneration of the biliary tree within damaged or diseased livers is a long-standing issue that remains unsolved in the medical community. Chronic conditions which lead to biliary degeneration, including forms of cholangitis and cirrhosis, are associated with most liver transplants in the United States [1]. The need to provide alternatives to transplantation is paramount to the advancement of hepatic medicine. The microenvironment of the liver that directs the generation and maturation of bile ducts has been difficult to recreate in an orderly or functional manner, and is cause for our interest in developing novel scaffolds which can serve as a platform to study these mechanisms and possibly lead to functional liver replacements in the future. We propose the design of a 3D-printed, hierarchically porous poly(lactic-co-glycolic acid) (PLGA) scaffold which has been infused with extracellular matrix-derived hydrogel for the study of cholangiocyte growth, differentiation, and organization. In this study, the PLGA component is intended to provide mechanical tunability, whereas the infused hydrogel is meant to serve as the conduit for directed cholangiocyte culture. Signaling factors commonly associated with other functions and tissues within the body have gained attention for their ability to manipulate the development of cholangiocytes. We are interested in investigating the regenerative effects of three such factors, GABA, FSH, and TGF-?1, in our 3-dimensionally oriented scaffold [2?4]. While other approaches have used melted poly (capro lactone) (PCL) as a support structure for 3D printed hydrogels, these scaffolds are mechanically stiff and unfavorable for implantation in or around soft tissue, such as the liver [5]. Additionally, other groups have investigated the formation of extrahepatic bile ducts in vitro, but we aim to better understand intrahepatic biliary regeneration, which is necessary for full liver function [6?9]. Despite studies investigating the biological mechanisms of intrahepatic duct regeneration, the unmet need of biliary tree tissue engineering for regenerating liver tissue is the primary motivation of this project [4,10]. Engineering nonparenchymal liver cells into separate vascular and epithelial tubular structures is unlikely to be achieved without employing the innate morphogenic quality of the tissues and cells in question in addition to novel biomaterial and cell patterning approaches. Our proposed work is intended to demonstrate a model system for the community as we collectively move toward more complex 3D organ engineering systems that more closely mimic native tissue for the purposes of eventual implantation.